1. Field of the Invention
This invention relates to the magnetic recording art and more particularly, to magnetic recording media which comprise specific types of lubricants contained in the magnetic layer thereof.
2. Description of the Prior Art
Small-size, portable home video tape recorders have been recently developed and reduced into practice. This type of video tape recorder is frequently employed for recording of outdoor activities. This in turn requires magnetic recording media which are proof against severe environmental conditions. For instance, they should stand use over a wide range of temperature. One of properties of magnetic recording media which are readily affected by a change of temperature is a travelling performance. The magnetic layer considerably increases in coefficient of kinetic friction especially under low temperature conditions, so that the travelling performance becomes poorer.
In order to solve frictional problems involved in magnetic recording media, it is common to add lubricants to the magnetic layer of the media. Typical examples of the lubricants include higher fatty acids, dimethyl silicone, and the like.
Although higher fatty acids exhibit good compatibility with binder resins in magnetic layer and show relatively good lubricating effects, they are apt to be adsorbed on magnetic particles. This leads to drawbacks that the acids are unlikely to ooze on the magnetic layer surface, thus reducing the effect of lowering the coefficient of kinetic friction of the magnetic layer surface and tending to give an adverse influence of temperatures on the layer.
Dimethyl silicone shows the great lubricating effect of the magnetic layer but has poor compatibility with resin components in the layer, leading to ready exudation of the silicone from the magnetic layer surface. When the magnetic recording medium having the magnetic layer on which the dimethyl silicone exudes is repeatedly used, its coefficient of kinetic friction gradually increases. As a result, the travelling performance and abrasion resistance undesirably lower. The exuded dimethyl silicone will cause magnetic heads and the like parts to be stained therewith, giving an adverse influence on recording and reproducing operations.
As substitutes for these higher fatty acids and dimethyl silicone, there have been proposed in Japanese Patent Publication No. 52-34924 and Japanese Laid-open Patent Application No. 57-92424 silicone compounds represented by the following formulas (A) and (B), respectively. ##STR2## Although these silicone compounds have an excellent lubricating effect and a coefficient of friction stabilized against the temperature change, they are not satisfactory in compatibility with resin components in magnetic layer.